CN107659362A - A kind of full light steganography method based on ASE noises and Wavelength-encoding phase-modulation - Google Patents

Abstract

The invention discloses a multi-bit wavelength coded phase modulation all-optical steganography method using ASE noise as a carrier. The ASE noise is distributed to each output port according to the wavelength distribution codeword through WSS to form each sub-carrier. The method of phase-modulating each subcarrier with the corresponding data sequence after the operation of "conversion" or "inversion" not only realizes the hiding of secret signals in the time domain and frequency domain, but also improves the reliability of authorized user communication while ensuring the communication reliability of authorized users. The spectrum utilization of the system is improved. Moreover, it is simple to implement, has good scalability, and the capacity of the key space is also greatly increased.

Description

An all-optical steganography method based on ASE noise and wavelength-coded phase modulation

technical field

The invention relates to the field of optical network physical layer security, and provides a wavelength-coded phase-modulated all-optical steganography system using ASE (amplifiedspontaneous emission) noise as a carrier. This system is mainly used in the hidden transmission of high-level information in all-optical networks.

Background technique

With its potential advantages such as high transmission bandwidth and high processing rate, all-optical networks have gradually replaced traditional optical networks and become the preferred technology for trunk communication networks. As the physical link layer in the entire communication system, the optical network is traditionally considered to have relatively high security guarantees due to its characteristics of closed and insulated transmission media and strong anti-electromagnetic interference capabilities. However, with the progress and development of various sabotage and eavesdropping technologies and equipment, and incidents of sabotage and attacks on optical networks have been exposed in recent years, the prejudice that optical networks have inherent security is gradually being broken. Moreover, the research and design of optical networks in terms of transmission, switching, control, and management are more concerned with transparency, openness, and interconnection. From the source, there is a lack of attention and research on security and confidentiality requirements, and this openness makes optical networks easy. being attacked. On the other hand, traditional information security technologies mainly focus on high-level encryption protocols, but high-level security mechanisms need to be built on the basis of low-level security. Therefore, physical layer security is the first barrier for the entire communication security. The communication network provides an irreplaceable security guarantee.

The all-optical encryption method that has been proposed so far is to first encrypt the original data to be transmitted into ciphertext (such as through XOR logic operations, etc.), and then transmit it in the optical fiber link after modulation. Only when the receiver has the correct key , the original data can be recovered through demodulation. Most of the current encryption methods use block encryption. If an eavesdropper records the ciphertext information for a long time, it is possible to crack the key through statistical methods, thereby attacking the entire system. Chaotic encryption uses the synchronization of the chaotic system at the sending end and the receiving end, and uses the parameters of the chaotic system at the sending end as the key. Although the chaotic encryption method has a large key space, it has high requirements on the consistency of the sending and receiving end system parameters. As long as there is a small mismatch, it may be difficult to establish chaotic synchronization, so the robustness is poor . On the other hand, these encryption methods do not realize the hidden transmission of secret information, which brings hidden dangers to the security of secret information. Quantum key distribution is to distribute keys through single photons, combined with the "one-time pad" encryption method to ensure the absolute security of private signals. However, limited by the noise and serious attenuation in the single photon transmission system, its transmission rate and transmission distance are very small.

All-optical steganography is to hide the secret signal to be transmitted in the public channel and system noise, that is, no one knows the existence of the secret signal except the sending user and the authorized receiver, so that the transmission security of the secret signal can be guaranteed. The early all-optical steganography method used ultrashort optical pulses as the carrier, and the modulated optical signal was fully stretched in the time domain through methods such as group velocity dispersion or spectral phase encoding, and the peak power dropped significantly until it was lower than the system The power of the noise so that the signal is drowned in the noise. At the receiving end, the original signal can only be demodulated and restored by correct dispersion compensation or spectral phase inverse coding. However, these all-optical steganography methods only realize the hiding of secret signals in the time domain. In the frequency domain, since the spectral width of the carrier is much narrower than that of the noise, and the peak value of the power spectrum is much larger than the noise, the eavesdropper can pass Spectrometers can easily find secret signals, so there is no hiding in the frequency domain. In order to solve this problem, the best way is to directly use the system noise as the carrier to transmit the secret signal.

So in recent years, an all-optical steganography method using ASE noise as a carrier has emerged. In 2013, Ben Wu et al. from Princeton University in the United States took advantage of the short coherence length of ASE noise to propose a phase modulation method using the optical path difference between the two arms of the Mach-Zehnder Interferometer (MZI) at the transmitting end as the key. The end uses MZI to correctly compensate the optical path difference between the two arms of the sending end, and then uses the method of coherent detection to demodulate the original data signal. In order to further enhance the security of the secret signal, the system uses a tunable optical delay line (OTDL) to generate a dynamically changeable optical path difference, that is, a dynamic key. However, the tuning rate of OTDL is very slow, usually on the order of seconds. If the eavesdropper has a fast search technology, when the average time for him to search for the key is less than the period of the system key change, he can obtain part of it through coherent demodulation. raw data information.

Therefore, in order to further strengthen the security of the system, it is necessary to design a steganographic method that can quickly reconstruct the key. In 2014, Huatao Zhu et al. from the Photon Information Technology Laboratory of PLA University of Science and Technology proposed a complementary coded optical steganographic system using the wavelength allocation codeword of the wavelength selective switch (WSS) as the key. Since WSS has microsecond-level reconfigurable time, it can realize fast reconfiguration of keys. The ASE noise after complementary coding and intensity modulation is similar to the original ASE noise in both the time domain and the frequency domain, but in a bit period, the modulated ASE signal only occupies half of the wavelength channel of the WSS, if the eavesdropper can By using a spectrometer to record the frequency spectrum of the modulated signal at multiple different bit periods, the existence of the secret signal can be discovered and the wavelength allocation codeword can be cracked, so as to obtain the secret data signal. In addition, this method uses all frequency slot channels of the WSS to transmit only one bit of data information in one clock cycle, and the spectrum utilization rate is low.

Based on the above analysis and comparison, the existing all-optical steganography methods have their own advantages and disadvantages. It is necessary to design a steganography method that can hide secret signals in both time domain and frequency domain, has the characteristics of fast and dynamic key changes, and has a large spectrum utilization rate. Aiming at the problems raised above, the present invention proposes an ASE noise-based multi-bit wavelength code phase modulation optical steganography method.

Contents of the invention

The invention designs a multi-bit wavelength coding phase modulation optical steganography method using ASE noise as a carrier. FIG. 1 shows a schematic diagram of an N-bit wavelength-coded phase modulation method. This method uses WSS to encode the wavelength of ASE noise to generate 2N sub-carriers, and performs phase modulation on the 2N sub-carrier signals after serial-to-parallel conversion and inversion operations on the secret data signals to be transmitted, and uses OTDL (tunable fiber delay Line) and VOA (Variable Optical Attenuator) control, so that the 2N modulated subcarriers achieve synchronization in the time domain and approximately equal power, and then are coupled with the signal on the common channel and transmitted in the optical fiber. At the receiving end, the authorized receiving user uses WSS to select the corresponding wavelength channel, and then uses coherent demodulation to restore the original data signal of the corresponding bit. This method can not only make the coded and modulated ASE noise cover all wavelength channels of WSS at any time, but also increase the spectrum utilization rate under the premise of ensuring the communication reliability and security of authorized users. In addition, compared with the original complementary coding intensity modulation method, the key space of this method is greatly increased.

Regarding the first point mentioned above, that is, the ASE noise after wavelength encoding and phase modulation can cover all wavelength channels of WSS at any time, the specific instructions are as follows:

In this method, the ASE noise component in each wavelength channel of the WSS will generate a time-varying phase shift, which is determined by the wavelength allocation codeword and the corresponding data sequence. This phase shift does not change the power spectrum of the wavelength channel component, so the spectrum of the modulated ASE signal is similar to the original ASE signal, and can cover all wavelength channels of the WSS.

For the second point mentioned above, that is, to increase the spectrum utilization rate under the premise of ensuring the communication reliability and security of authorized users, the specific instructions are as follows:

Compared with the single-bit wavelength coding system, the multi-bit wavelength coding phase modulation system can use all the wavelength channels of the WSS to transmit multiple bits of data information in one clock cycle, and the spectrum utilization rate has been improved. On the other hand, the power of each subcarrier is also reduced, and the reduced subcarrier power can be compensated by increasing the gain coefficient G of the erbium-doped fiber amplifier (EDFA). Although increasing the gain factor G will introduce more additional noise (unmodulated ASE noise), when the modulated ASE carrier power value is greater than -10dBm, that is, when the beat frequency noise is dominant, the modulated ASE signal After EDFA amplification, the deterioration degree of SNR has nothing to do with the gain coefficient G of EDFA. Therefore, the demodulation quality of the licensed receiver is almost the same as that of the single-bit system, so the system does not threaten the reliability of the licensed user's communication while increasing the spectrum utilization.

Regarding the third point mentioned above, that is, compared with the original complementary coding intensity modulation method, the key space of this method is greatly increased, and the specific description is as follows:

In this method, even if the eavesdropper knows that there is a secret signal transmitted in the system, he needs to know the specific "key" in order to demodulate the secret signal. The key includes not only the wavelength allocation codeword of the WSS, but also the delay line length of the corresponding branch at the sending end. The key changes from the original one-dimensional space to the two-dimensional space, and the capacity of the key space is greatly increased. In addition, the possible wavelength allocation codewords of WSS have also been expanded due to the introduction of multiple bits. For an N-bit wavelength coding system, the wavelength allocation codeword randomly divides the M wavelength channels of the WSS into 2N channels, and each channel contains wavelength channels, the number of possible selections is Compared to the single-bit complementary coding system's greatly improved.

For the phase modulation and coherent demodulation of each ASE subcarrier after wavelength encoding, the specific instructions are as follows:

For each ASE subcarrier after wavelength encoding, it is a wide-spectrum signal with a very short coherence length, so the traditional continuous wave phase modulation and delay interference demodulation method cannot be used. The phase modulation and solution of this kind of wide-spectrum carrier The tuning principle is shown in Figure 2. At the sending end, the carrier wave is first divided into upper and lower branches with equal power by MZI (Mach-Zehnder Interferometer), and an optical fiber delay line L _X is introduced into one of the branches, and then the carrier signal of the branch is used with data Perform phase modulation. In order to make the modulated ASE signal have a similar spectrum to the original ASE noise, the length L _X of the introduced fiber delay line should be greater than the coherence length L _c (372um) of the ASE noise. Otherwise, the optical signals of the upper and lower branches will coherently superimpose. For the same optical path difference, different wavelengths will produce different interference results, which will change the spectrum of the original ASE noise. In FIG. 2 , the upper branch of the MZI at the transmitting end is "phase-modulated carrier", and the lower branch is "unmodulated carrier". At the receiving end, MZI is used to introduce a fiber delay line _LR in another branch to compensate the optical path difference between the upper and lower branches of the MZI at the sending end (namely "phase-modulated carrier" and "unmodulated carrier"). When |L _X -L _R |<L _c is satisfied, the "phase-modulated carrier" and the "unmodulated carrier" are coherent, and the digital signal can be demodulated by coherent detection (such as homodyne balanced reception).

In summary, the present invention utilizes the ASE noise in the optical network as the carrier to transmit the secret signal, and at the same time realizes the hiding of the secret signal in the time domain and the frequency domain, adopts a dynamic key that can be changed quickly, and ensures the reliable communication of authorized users. At the same time, it also improves the spectrum utilization of the system. The method is simple to implement and low in cost, and can be used for secure communication of signals with higher confidentiality in optical networks.

Description of drawings

Fig.1 Schematic diagram of N-bit wavelength-encoded phase modulation steganography method.

Fig. 2 is a schematic diagram of a phase modulation/coherent detection method for each ASE subcarrier.

Fig. 3 is a schematic diagram of a two-bit wavelength coded phase modulation steganography method.

Detailed ways

In order to make the purpose, technical method and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Implementation:

This embodiment is based on the two-bit wavelength-coded phase-modulated all-optical steganography system shown in FIG. 3 , where the WSS includes 96 wavelength channels. It mainly explains the process of secret signal to realize hidden communication. The specific workflow of this implementation is as follows:

1. Allocate the 96 wavelength channels of WSS to 4 channels of signals according to four wavelengths (assuming code1, code2, code3 and code4 from top to bottom), each channel contains 24 wavelength channels;

2. The ASE noise of the system is encoded by the WSS wavelength to form 4 ASE subcarriers (assuming that they are the 1st, 2nd, 3rd, and 4th subcarriers from top to bottom), and each subcarrier signal passes through the upper branch with a fiber delay line and the MZI of the phase modulator, as shown in Figure 2. Assume that the lengths of the fiber delay lines introduced by MZI in the 4 carriers from top to bottom are L _X1 , L _X2 , L _X3 and L _X4 respectively;

3. After serial-to-parallel conversion of the secret data to be transmitted, two subsequences of odd bits {b _2k } and even bits {b _2k+1 } are generated, and these two subsequences are reversed bit by bit to generate with Two new sequences, use these 4 sequences to phase modulate the 4 subcarriers respectively (for example, use {b _2k+1 } to modulate the 1st subcarrier; Modulate the second subcarrier; {b _2k } modulate the third subcarrier; Modulating the 4th sub-carrier);

4. Pass the sub-carrier signals after wavelength encoding and phase modulation respectively through VOA (to make the power of each sub-carrier modulation signal approximately equal) and OTDL (to make each sub-carrier modulation signal reach domain synchronization), and then pass through two 50: A 50 coupler is coupled into a modulated ASE noise signal;

5. Coupling the modulated ASE noise signal with the signal of the public channel through a coupler, and then transmitting together in the optical fiber;

6. At the receiving end, because the carrier of the public channel is continuous light, and the power is much higher than the ASE noise, the public channel can directly use the corresponding demodulation method to achieve demodulation (that is, if the public channel uses intensity modulation, the receiving end Just use the method of direct detection to demodulate, if phase modulation is used, the receiving end adopts the method of delay interference to demodulate);

7. For secret signals, the authorized receiver needs to assign codewords according to the wavelength of the sender, select the wavelength channels corresponding to code1 and code3 with the WSS configured the same as the sender, and filter out the wavelength channels occupied by public channels (public channel’s The carrier is continuous light and only occupies 1 wavelength channel). Then accurately match the optical path difference introduced by the MZI at the sending end of the first and third subcarriers, and finally use the homodyne balance detection method to realize phase demodulation, and restore the original data after parallel-to-serial conversion.

Claims (4)

1. a kind of more bit Wavelength-encoding phase modulated light steganography methods based on ASE noises, main process is included (with N-bit Exemplified by Wavelength-encoding phase modulation system)：

A. it is 2N subcarriers by ASE noises are produced in EDFA by WSS points；

B. to each subcarriers, the data sequence corresponding to carries out phase-modulation, and the signal after then each road is modulated is coupled into " signal ASE "；

C. in receiving terminal, authorized receiver is using similarly configuring with transmitting terminal identical Wavelength Assignment code word and with transmitting terminal WSS, the respective wavelength channel selecting for modulating each bit is come out, then tick-tack is recovered after demodulated and parallel serial conversion.

2. method as claimed in claim 1, WSS M wavelength channel is randomly assigned WSS's according to Wavelength Assignment code word 2N output port, the subcarrier of each port output includeIndividual wavelength channel.

3. method as claimed in claim 1, initial data is obtained into 2N subsequence by serial to parallel conversion and after negating computing {b_Nk},{b_Nk+1},…,{b_Nk+(k-1)AndPhase is carried out to 2N subcarriers respectively Modulation.2N roads modulated signal reaches the approximately equal of power spectrum and temporal synchronization by VOA and OTDL, then passes through coupler " signal ASE " after synthesis modulation.

4. method as claimed in claim 1, with the WSS similarly configured with transmitting terminal N number of output port, it will be used to modulate respectively Sequence { b_Nk},{b_Nk+1},…,{b_Nk+(k-1) Individual wavelength channel chooses.The method of coherent demodulation is recycled to obtain phase The Serial No. answered, then by recovering secret data signal after parallel serial conversion.